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Demonstration of High Geospatial Accuracy Achieved by a Fixed Wing UAV | QuestUAV News

Demonstration of High Geospatial Accuracy Achieved by a Fixed Wing UAV

1 (3cm) pixel accuracy across 2 Km grid using a QuestUAV Surveyor Pro UAV

1 Survey Objectives and Deliverable Items

The purpose of this survey was to achieve a high accuracy topographic map and Digital Elevation Model (DEM) of a study area Post Processing Mapin a foreign country that:

(a) was managed by an independent and competent third party, totally independent to QuestUAV.
(b) provided the opportunity to compare QuestUAV performance against other UAV vendors such as EBEE, Dronematrix, Trimble, UAVER

The survey was conducted in August 2015 in South Korea, under the auspices of LX, the South Korea governmental survey agency.

The agency laid out a set of twelve Ground Control Points (GCP) spread across the 1200m x 1200m survey area.

To check consistency the agency also laid out six Control Points (CP’s) across the survey area with the intention that these be used to independently confirm the accuracy of the survey after it had been completed. The survey has returned excellent results with an average accuracy of 3cm (1 pixel) across the survey area, using the control points for validation.
For this survey we have focussed simply on land mapping and elevation analysis. It is worth noting that in addition to this a survey can return a vast array of data in terms Copyright © QuestUAV 2015 All Rights Reserved of land mapping, infrastructure, elevation change, agriculture, social change, road usage, boundaries, forestry, floodplain and drainage, erosion, crop volume and many more subject analysis.
In accordance with our agreement with the agency, QuestUAV has the following deliverables associated with this survey. (All deliverables are available through our Geotech department, identified at the end of this document.)
  • Survey report (this document), including a survey description, a summary of the results and a basic image analysis.
  • A3 map of the survey area (PDF format).
  • Image processing report (Agisoft Photoscan).
  • Agisoft Photoscan project file (PSZ format).
  • Natural Colour Image with 3cm spatial resolution (GeoTiff, KML and ECW format).
  • Digital Elevation Model with 6cm spatial resolution (GeoTiff, KML and ECW format).

South Korea

Ground Image of the Northern sector of the Survey Area

2 About the Survey, and the Equipment Used

The QuestUAV survey was undertaken on 26 August 2015 with a standard QuestUAV Surveyor Pro (see front page for the UAV) in a built up area close to Jeonjo, Southern Korea. The UAV was equipped with a gimballed Sony A6000 camera operating on a 2 second trigger. 1,350 images were acquired in total with an overlap of 80% in-flight and 60% side lap. The figure below shows the flight path and indicates the image overlap. (The irregular area to the top is the result of high ground reducing the overlap.)

The area of survey has 13 GCP’s and 6 control points for accuracy assessment and is contained within approximately a 1 square kilometre grid.

The UAV took off from the school grounds in the centre of the survey area and flew the area once EAST-WEST and then routed to a NORTH-SOUTH grid, all within a single fight. The UAV returned to the launch area for a parachute landing. The flight took approximately 45 minutes.

A crew of two was used for the survey; a pilot (N King) and a laptop commander (R Moore). The UAV was visible throughout the flight. Flight was autonomous from take off until the decision for parachute landing preparation.

                  Q-200 Surveyor Pro Launch Aerial Image

Launching the QuestUAV Surveyor 200 (L) Natural colour image of the study area showing distribution of ground control points (R)

3 Image Processing

Pix4D ScreenshotAn A4 sheet was laid on the ground with an identifying mark in the centre of the sheet. The centre was referenced using high accuracy DGPS survey instruments returning mm accuracy.The image processing was
completed in Agisoft Photoscan. The computer used took approximately 18 hours to complete the dense point cloud creation – the longest part of the processing.

Input for the image processing were the following 3 datasets:

  • 1,350 UAV raw images
  • QuestUAV log file (image name, latitude, longitude altitude, yaw, pitch, roll)
  • 19 ground control points for geo-rectification

A total area of 2.3 square kilometres has been processed. Details on the image processing can be taken from the Agisoft Photoscan Processing Report, which is part of our deliverables.

4 Image Accuracy

The outcome of the image processing was a high resolution Natural Colour mosaic with a spatial resolution of 3cm and a Digital Surface Model (DSM) with a spatial resolution of 6cm.

The accuracy error, calculated through the CP’s, throughout the mosaic was on average one pixel (ie the same as the spatial resolution).

The processed Natural Colour Image shows:

  • Land usage: Spread of buildings. Building and land boundaries can be clearly identified. Heights of buildings can be assessed.
  • Power lines routing and condition.
  • Roads and highways: Sizes, dimensions, road surfaces, barriers, road marking, dangers from signals and signage
  • Agricultural information: Field boundaries and field roads can be identified. Crop types, crop status and crop health can be assessed. Presence of illegal crops or illegal usage of land can be detected.
  • River boundaries and conditions: Conditions of river structures, flow of water and water colour.

                                                                                                             Detail from the Natural Colour Image

                                Drone Aerial Image Crops Drone Aerial Image

                                                       Different crop types of agricultural areas can be easily identified.(L) Markings on a road intersection. (R)

4.1 Digital Elevation Model

Elevation ModelA Digital Elevation Model (DEM) is a digital representation of the elevation of a terrain. Each pixel of a DEM contains an elevation value. Our
DEM of the study area shows a minimum elevation of 45 meters and a maximum elevation of 105 meters above sea level. The terrain rises from the centre line of the study area in both directions, Northwest and Southeast.

Digital elevation models are the basis for in-depth terrain analysis and hydrologic calculations, like for example:

  • Determining the slope of roads
  • Calculation of height profiles along roads
  • Derivation of contour lines
  • Calculation of hill slopes and determination of aspects
  • Determining watersheds and stream networks
  • Modelling flow accumulation and runoff volumes
Flight Data

Please note there is no universal usage of the terms Digital Elevation Model (DEM), Digital Terrain Model (DTM) and Digital Surface Model (DSM) in scientific literature. In most cases the term digital surface model represents the earth's surface and includes all objects on it. In contrast to a DSM, the digital terrain model represents the bare ground surface without any objects like plants and buildings

In our case we have produced a Digital Surface Model (DSM), showing the elevation of all objects on the ground. A DSM can be used as basis to derive a Digital Terrain Model (DTM).

The accuracy of the DEM was assessed by comparing the elevation values of the ground measurements (GCPs and CPs) with the DEM values at the ground control locations. The table below shows how good the elevation of GCP and DEM match. The average difference is between 0 and 3 cm.


5. Land Mapping and Elevation Analysis

The survey can return a vast array of data in terms of land mapping, infrastructure, elevation change, agriculture, social change, road usage, and many more subjects. The following sub-chapters show examples of an in-depth data analysis.

5.1 Mapping the Location and Size of Buildings
Mission PlanningThe location and size of buildings or other objects on the ground (field boundaries, ponds, parking areas, etc.) can be precisely determined on the basis of the Natural Colour Image.

Each pixel of the Natural Colour Image has a unique geo-coordinate and represents an area of 3 cm x 3 cm. With such a high spatial resolution, roofs can be easily identified and digitized inside a Geo-Information System (GIS). A GIS allows to automatically calculate the roof area.

Example of mapping greenhouses and determination of roof sizes.


5.2 Determining the Slope of a Road

Digital Elevation ModelThe slope is a measure of the steepness of a road and can be determined on the basis of a Digital Elevation Model (DEM). Slopes are calculated by determining the change in elevation along two points. Height profiles allow us to understand the elevation changes and show the ups and downs along a track. The figure below shows the height profile along a road section in the north-eastern corner of the study area.

The elevation changes in south-north direction from 49.2m to 53.8m, along a length of 346m. According to the common slope formula (slope = rise/run x 100), the slope of the road section is 1.3 %.

Please visit our dataset page for more examples - Datasets

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Multiple Datahawk Delivery

DATAhawk Fleet Arrives in South Korea For Large Scale Cadastral Survey Work

New fleet of Q-100 DATAhawks arrives in South Korea

A fleet of DATAhawk mapping UAVs have arrived in South Korea, ready to perform mapping duties as part of an ongoing, large-scale cadastral survey mission by government departments.

Multiple Datahawk Delivery
Multiple Datahawk Delivery

A nationwide effort to create datasets that can be used by government and citizens looking to monitor and manage a wide range of land uses has been underway for some time

The DATAhawk fleet will bolster those efforts, with a flight time of up to an hour and a QX series imaging sensor giving a 3.2cm GSD - allowing fine ground details to be captured easily. The aircraft is easily launched by hand or from the AirDock system (seen below) and comes as standard with parachute recovery for landings.

DATAhawk mounted on Airdock
DATAhawk mounted on Airdock

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Sequoia, QuestUAV and Pix4Dmapper-Ag - the dawn of a new era in multispectral imaging |  1

Pix4D User Workshop in Brisbane

HELImetrex - a QuestUAV Australian partner - is hosting the first Pix4D User Workshop in Brisbane.

This is the perfect opportunity to meet face-to-face with HELImetrex experts and develop your knowledge.

The course runs on September 7th, 8th and 9th.

Course Schedule

Day 1 (from 9AM to 5:30PM)

  • Pix4Dmapper Applications
  • From Images to 3D Points (Theory)
  • Pix4Dmapper Outputs (Compatibility with CAD/GIS software)
  • Georeferencing and Accuracy
  • Pix4Dmapper Best Practices
  • Pix4Dmapper Basic Demo
  • Precision Agriculture
  • Hardware and Processing Time
  • Future plans of Pix4D
  • Q&A

Day 2 (from 9AM to 5:00PM)

  • Pix4Dcapture
  • Flight Planning
  • Flight 1 (Copter)
  • light 2 (Fixed Wing)
  • Hands-on exercise session:
    • Create a project
    • Add Manual Tie Points/GCPs
    • Evaluate the Quality of the project
    • Add Scale Constraints
    • Merge 2 projects
  • Q&A

Further Information:

Q: What level of experience is the Workshop intended for?
A: This workshop is geared towards beginner and intermediate users. It covers topics such as best practices for data acquisition and the different processing options. While the workshop can be attended without any previous exposure to Pix4Dmapper, we recommend having processed at least 1 project to get the most out of the event.

Q: Is lunch included in the Workshop price?
A: Lunch, coffee/tea, snacks and water are included in the price.

Attending the Workshop also gives you access to a 30-day license of Pix4Dmapper Pro


HELImetrex Pty Ltd
Unmanned Aerial Surveys
Australian QuestUAV Reseller
Office Direct: +61 (07) 3040 2354

For more information, registrations and workshops near you:

Brisbane Workshop Information Pack

Pix4D Workshops

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ppk blog image

QuestUAV Launch New Blog (PPK and Beyond) | QuestUAV News

QuestUAV Launch New Blog (PPK and Beyond)

As we run through the process of testing and proving our new PPK product, Nigel King - the drive behind the company - felt the best way to convey the accuracy and testing schedule information was to run a blog with fuller details and faster status updates.

One week later - QuestUAV present the launch of our new Technical Overview Blog, which will begin with PPK and run on with insider details of our other products and services as they present themselves.

For now, the plan is to cover PPK with the topics:

  • What is really achievable in terms of Accuracy and Ease of Use?
  • The benefits of a PPK System
  • The Big Challenges to Overcome
  • Case Study: A Typical PPK Survey
  • Verification: Independent Assessors
  • Our White Paper: The Final Evidence
  • The QuestUAV Development Team
  • Post Processing PPK Data
  • Base Stations
  • Factors Affecting PPK Accuracy
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Drone Chasers Mobile Ops

Drone Chasers – Mobile Ops

Mobile Operations - The Art of Chase Vehicles For Extended VLOS Missions

Whilst autonomous UAVs are incredibly useful for surveying, they are not totally "fire and forget" in operation - you need to have a flight team to manage the mission as the aircraft performs its flight plan. This is generally because of safety and other flight regulations - once launched the UAV itself is perfectly capable of flying its path and landing automatically.

Drone Chasers
Drone Chasers Mobile Ops

These flight regulations, the world over, tend to include sections that define how far a UAV can fly from the majority of qualified handlers and remain in compliance. Within the UK - that distance in most circumstances is a VLOS one - Visual Line Of Sight - and extends to 500m. Missions over a larger area than that effective 1km in diameter around the flight team require multiple flights or a mobile operations team.


Planning, Preparation and Mission Modelling

Drones Chasers Ops Order

UAV flight management already needs good training and certification and even in a fixed location requires very close attention when the mission is underway. When mobile, that requirement increases dramatically. Planning each stage of the flight is the best first step.

Make allowance for the chase teams to be slower than the UAV. Ensure you have a scout ahead of the main crew to watch for unexpected changes since the initial route checks.

Drones Chasers Route Recce

Once the mission plan is in place, there is no substitute for modelling the chase process with the flight team to ensure they have good procedures for any eventualities that could arise. Safety is aided by sensible preparations - watching and listening to procedures for communication amongst vehicles and team members will help standard flight operations to become more second nature and leave the team more capable to meet the challenges of a changing situation during the real flights.

For The Road

Careful vehicle selection and preparation is needed to mitigate the risk of mechanical issues during the missions. Larger cars to carry spares and ancillary crew members are handy, but open-topped vehicles afford the flight team much better all-round views.

Good driving skills and well defined communications procedures are essential.

Drone Chasers Vehicle Prep

Environmental Interference

Drone Chasers Mobile Ops

Roving tests with the chase crews and the flight team are important. Checking the route for GPS and telemetry interference gives the opportunity to observe the moment-to-moment conditions and plan ahead for any problem locations.

On The Road - Manage Mission Leg Distances

"Fly - loiter - fly" is the best mechanism when laying out a flight-plan - pick air locations for loitering the UAV that match ground points for temporary static pilot positions with good visibility for the next flight leg.

Drone Chasers AutoPilot Monitor
Drone Chasers AutoPilot Monitor
Drone Chasers Mobile Ops
Drone Chasers Mobile Ops

Keeping a contingency charge percentage in the UAV batteries during stage planning is important for normal missions - doubly so for mobile ops, where ground conditions for the chase/flight teams could necessitate an extended loiter.


Mobile Ops certainly has its hazards - but these can be mitigated and the advantages are longer range surveys with fewer mapping flights.

Important requirements are:

  • Fully planned, team-modelled and manageable flight legs - with dry-runs for all involved teams.
  • Capable vehicles and drivers - including wide visibility options for the actual pilot/commander crew.
  • Prior route runs to familiarise chase crews with ground conditions and to assess potential interference issues.
  • Good communication procedures - cover as wide a range of possibilities and test them thoroughly during dry-runs.
Drone Chasers Route Analysis

Successful completion of a 19km mobile ops leg.

Q200 Drone Chasers

Happy chase team - ready for next mission.

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Twin Sensor Gimbal

Know Your Gimbals

Know Your Gimbals


A gimbal is, simply put, a cradle that allows the object contained within it to rotate about a particular axis (backwards and forwards, or left and right, or side to side - known in technical terms as pitch, roll and yaw). Used for a sensor within an aircraft, a gimbal for any particular axis allows the sensor to continue to point directly at the ground, while the aircraft itself is manoeuvring around that same axis.

Twin Gimbal

Without the gimbal, the sensor remains pointing out from the aircraft in whichever direction it was installed. Images taken as the aircraft moves about an axis will then be oblique instead of having all parts mostly parallel to the ground. This lowers the apparent resolution in the areas further away from the sensor in each image, as each pixel is covering a larger ground space at an offset angle, giving less for the processing software to work with for any given image overlap.

With the smooth, fluid movement of a gimbal, any small motions of the aircraft (including types of vibration) are countered - stopping most blurring issues. Extra gel is placed in QuestUAV gimbals, interspaced with the sensor mount, to reduce other non-axis vibrations to a minimum.


QuestUAV are one of the only fixed-wing UAV manufacturers to include gimballed sensors across the full range of aircraft. The value of having gimbals for your sensors and what they bring to your image collection missions is hopefully a little clearer now. Understanding the difference makes it difficult to consider aircraft without them (even if that means asking specifically for them to be added as an optional extra).

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QuestUAV Provide Own PPK Solution For Q-200

QuestUAV Provides Own PPK Solution For Q-200 Surveyor UAV


QuestUAV Own PPK

PPK (Post-Processing Kinematic) provides much higher accuracy in GPS location when stored against images taken in a UAV. Standard GPS signals are accurate to 10's of metres - PPK increases that accuracy to cm-levels. On board the Q-200 UAV, PPK eliminates the need for physical Ground Control Points (GCP) that are often used to gain high accuracy in surveys. This saves hours of mission planning and setup time, physically measuring location points and walking the survey site for placement.


GCPs – The underestimated part of a UAV survey

Surveys involving GCP generally run like this:

  • Initial site is viewed to establish useful locations for Ground Control targets.
  • Each location is visited with a GCP and a Differential GPS receiver to accurately place the target.
  • Targets may need revisiting before survey takes place.
  • Locations are stored for post processing reference.

In most cases - up to half of the mission time is taken up with GCP placement. GCP targets may shift or collapse with changing weather conditions – requiring the original placement to be repeated (often wasting up to an hour of survey setup time); coastal surveys can suffer from tidal changes and cliffs make it difficult to place GCPs across the survey area; general survey ground conditions can make it difficult to secure GCPs - quarries are a good example of difficult, variable ground surfaces.


The advantage of PPK - Overcoming GCPs

The PPK solution offered by QuestUAV uses a higher performance, highly-accurate receiver placed within the aircraft - following more than 10 GPS satellites at any given time and storing location information against the triggered images taken. Combined with differential signal information collected by the fixed position Ground Station (which stores signal drift and signal error values), the image locations are recalculated to a much higher accuracy – down to centimetre level in x, y and z direction.

QuestUAV Own PPK

Compared to RTK (Real Time Kinematic), PPK also eliminates the need for a real-time data link with a fixed reference station during the flight, whilst guaranteeing RTK cm-level position accuracy of the images once post-processing has taken place, after the UAV lands. This simplifies the UAV set-up, reduces the requirements and power drain on-board and eliminates any loss of accuracy in data due to potentially unreliable radio links - which often plague RTK UAV operations.

The Q-200 Surveyor Pro is available with PPK at purchase or as an upgrade to an existing aircraft with the provision of just the PPK QPod.

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Flight Team in Truck

Long Range MicaSense Agronomy Surveys

Long Range MicaSense RedEdge Agronomy Surveys

Q-200 and Q-100 Aircraft Are Put Through Their Paces In Agricultural Survey

Long Range Flight Op

This long range agronomy survey was part of a mission in the English countryside. We regularly fly test and demonstration missions across the UK. A multiple airframe survey demonstration flown for Hummingbird Technologies was no exception.

The survey took place over 2 days, with both a Q-200 AGRI MicaSense UAV and a Q-100 DATAhawk MicaSense UAV. Each airframe is equipped with the MicaSense RedEdge multispectral sensor suite, capable of detailed multiband imaging across 5 discrete spectral bands.


Aerial Field

The survey site consisted of agricultural research samples and was imaged using both airframes using a 3-person flight team - 1 pilot, 1 commander and 1 spotter/driver for mobile operations.

On day 1 the Q-100 DATAhawk missions were repeated at different altitudes to demonstrate flight performance and MicaSense image quality. The DATAhawk covered 325Ha during a 42 minute flight at 400ft with a 70% overlap.



Day 2

Day 2 missions were designed to showcase the endurance of both the Q-100 DATAhawk and the similarly RedEdge-equipped Q-200 UAV. The Q-200 required only two flights to cover 730Ha at 400ft with 70% overlap. Parachute landings were performed in each case with a 46 minute flight time (per flight). Mobile ops were used to ensure Line of Sight requirements were adhered to.

Long Range Flight Op

Mobile Ops vehicle and crew


Final Analysis

Once processed, the imagery from both days' missions will form the basis of high quality NDVI and RedEdge Indices, which will be correlated and compared with agricultural information, such as LAI (Leaf Area Index), crop density and nitrogen uptake.

Clients on-site were very pleased with the endurance and performance of both the Q-200 and the Q-100 DATAhawk, especially when considering the high winds that were present during the surveys days.

Thermal Image

MicaSense RedEdge Image Stack

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Mapping Image

Technical Services For Imagery Analysis Available

Technical Services For Imagery Analysis

GIS, Image Processing and other services

The best and most sophisticated UAV equipment is of no use when, at the end of the flight, nobody can competently read the information behind an image. Image analysis can become quite a complex task, especially when multi-temporal and multi-spectral information is involved.

QuestUAV has many years’ experience with the interpretation of aerial images for various applications. We continuously expand this knowledge through close cooperation with our customers from different industries and via in-house research projects.



Technical Services

QuestUAV offers a wide variety of training courses, from beginners through to professionals, to learn GIS software and to improve GIS skills and understanding in aerial image interpretation. We train our clients in the open-source software - QGIS. Advanced courses are also given in GRASS GIS, SAGA GIS and GDAL.

GIS Service


Image Processing

Mapping Image

Our processing experts provide training in industry-standard photogrammetry software - Pix4Dmapper and Agisoft PhotoScan. Learn how to use the software packages to create beautiful orthomosaics and 3D models. Get to know the workflows for generating virtual flythroughs and translating multispectral UAV data into valuable index maps, such as NDVI or SAVI.

Image Process 


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Q200 Drone GGP

Congratulations Team GGP for Successfully Completing the QuestUAV Training

After Seven Days Intensive Flight Training The GGP Team Is Ready For Their First Survey Adventure

30,000 Hectares of Tropical Fruits Need To Be Mapped!

Q200 GGP in Flight

More Than 25 Takeoffs And Landings

After seven days of intensive training, the flight crew at GGP (Great Giant Pinapple) is ready to complete their own flight missions without supervision of the QuestUAV trainers. During the past week the team has practiced the whole mission workflow over and over again, including not only flight practice but also safety assessment, flight planning, site setup, UAV maintenance, camera preparation and data extraction.

The two Q-200 Agri-Pros have been launched and landed more than 25 times. The GGP crew has learned how to fly in different modes (auto and assisted) and how to land their QuestUAV drones with both methods, parachute and belly landing, on different surface types (matured pineapple, young pineapple, knocked down fields, roads).


Q200 Drone GGP

A Big Mission Ahead

The QuestUAV training was just the start of a larger survey mission and certainly a busy time for the new flight crews. 30,000 hectares of pineapple, banana and other tropical fruits are waiting to be mapped by the crew and analysed by GGP's agricultural and GIS experts.

UAV images, especially NDVI maps, will be used for the assessment of plant vigor and crop status, disease detection and identification of canopy gaps. Further, UAV-based elevation models will become the basis for developing a better drainage system for the entire plantation.


Thanks To All Helping Hands

The QuestUAV team, especially our trainers Nigel and Stuart, would like to thank GGP for their outstanding hospitality and the dedication of the whole crew to make this training week a success. Special thanks goes to Nanda Pratama (himself a QuestUAV pilot in Indonesia) for his translation work and training support.

Nigel and Stuart, now on the way back home, will bring many impressions and perspectives back to the QuestUAV workshop and we are looking forward to hear more stories from Indonesia.

Nigel King & GGP

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